1. Field of the Invention
The present invention relates to a noise suppression component selecting method and program, and more particularly, to a noise suppression component selecting method and program for selecting one of a plurality of noise suppression components for suppressing noise in, for example, a digital circuit.
2. Description of the Related Art
A noise analysis method for a digital circuit including digital ICs (integrated circuits), a noise suppression filter, and a transmission line is known in which an input signal to the digital circuit is expanded into a series of sine waves by Fourier expansion. In this method, circuit constants of the digital ICs, the noise suppression filter and the transmission line are input to a computer having a noise analysis program installed therein so as to determine the transfer function of the digital circuit. Based on the transfer function of the digital circuit and the Fourier-expanded input signal, a frequency-domain output spectrum of the digital circuit is obtained. The output spectrum is transformed into a time-domain output waveform by an inverse Fourier transform.
In this analysis method, an input signal, which is subjected to Fourier expansion, is expressed in terms of a series sum of sine waves, thus enabling circuit analysis by simple linear computation. Therefore, the signal waveform of the digital circuit is easily determined. Once circuit constants of a noise suppression filter are stored as data, the effects of the filter are simulated simply by selecting a filter type (see, for example, Japanese Unexamined Patent Application Publication No. 2001-265848).
Generally, circuit analysis apparatuses analyze a signal waveform of a digital circuit including a noise suppression filter to analyze noise suppressing effects of the filter. In order to select a filter suitable for the digital circuit, several filters which are expected to have noise suppressing effects must be selected and analyzed to determine the filter to be used from the selected filters by comparing signal waveforms.
When a filter is incorporated in a circuit, the current in the line into which the filter is incorporated is suppressed, and noise is reduced. However, this also affects a signal transmitted on this line, and the signal waveform can be distorted. In comparing analyzed signal waveforms, therefore, such an influence on the signal waveforms must be considered in addition to the noise suppressing effects. Thus, a filter suitable for the digital circuit must be selected in view of both the noise suppressing effects and the influence on signal waveforms. In other words, the filter must be selected empirically and intuitively. This is very difficult for persons unfamiliar with noise countermeasures, and it takes a long time to determine which filter is suitable for the digital circuit.